The present invention relates to locking apparatus for electrical connectors, and more particularly, to a twist-lock connector assembly for maintaining engagement between an engaged electrical plug and a socket.
When using electric powered appliances or power tools, it is necessary to maintain firm engagement between an engaged electrical plug and a wall outlet or power box in order to ensure an uninterrupted source of power to the appliance or power tool. Unintentional unplugging of an engaged electric power cord from a wall outlet can cause frustration and contribute to decreased productivity. For example, most people have experienced the common frustration of having the power cord of a vacuum cleaner unintentionally pulled loose from the wall socket several times while vacuuming.
As a further example, a computer plug which comes loose from its connection to a wall socket can result in loss of data. As another example, construction workers at a job site experience production losses each time they must replug a power tool that has come loose from a wall socket or power box during use.
Various techniques and devices have been proposed for ensuring engagement between an engaged electrical plug and wall outlet or power box. For example, in accordance with one prior art technique, the electrical plug is provided with a metal loop or fork tongue flange which is designed to be fastened by a screw to the center hole of the cover plate of the electrical outlet.
A disadvantage with this technique is that the cover plate center screw be loosened each time the electric plug is to be engaged or disengaged from the wall socket. Thus, this technique is extremely impractical for uses in which the electric plug will only be engaged for short time periods, such as is the case with the use of vacuum cleaners, gardening tools, power tools, etc. Further, this technique requires use of a screw driver each time the electric plug is to be locked in engagement with and unlocked from engagement with the wall socket. Further still, in the case where the electric plug to be engaged is a three prong plug, the presence of the third xe2x80x9cgroundxe2x80x9d prong of the three prong plug means that the plug can only be inserted into the wall socket in one orientation. Since there is usually only one center screw hole located between the two socket access openings of the cover plate, only one electric plug having the metal loop or forked tongue flange can be screwed in place to the wall socket at a time. Accordingly, a connector arrangement for securing an engaged electric plug to a wall socket which does not require use of additional tools to make the locking connection and which can lockingly engage more than one electric plug to the respective socket portions of an electrical outlet at a time would be a big advance in the art.
In the case of exposed outlet boxes of the type commonly found on boat docks, it is the common practice to use leather straps, string or even tape to ensure that an engaged electric plug remains connected to the socket portion of the outlet box. It is also the common practice to bend or deform the conductor prongs of an electric plug to create a tighter fit inside the outlet. Obviously such practices are only temporary fixes and do not provide a long lasting secure engagement between and engaged electric plug and an electrical outlet.
My previous approach to solving this problem is disclosed in U.S. Pat. No. 5,344,333. This approach proposes to use a rotatable cylindrical sleeve for twist-locking an engaged electric plug to a cover plate of a wall outlet. In this design the cylindrical sleeve is provided with a first end adapted for snap fit insertion within a socket opening of the cover plate and a second end provided with grooves along an inner cylindrical surface thereof. The electric plug is provided with a circular face plate having threads formed along its outer surface. In use, the plug is engaged within the socket and the sleeve is rotated such that the grooves of the sleeve lockingly engage with the threads of the face plate on the electric plug.
While my earlier design works well and offers many advantages over the prior art techniques discussed above, there is still a problem since dirt and debris tends to collect in the sleeve over time and this can inhibit positive locking engagement. Also, in my earlier design, two hands are required to complete the locking engagement between the engaged electrical plug and the wall outlet. Accordingly, a twist-locking connector arrangement which overcomes these problems would be extremely desirable.
It is therefore a principle object of the present invention to provide a simple, low cost twist-lock connector assembly for securing an engaged electrical plug to a wall outlet or power box.
It is a related object of the invention to provide a twist-lock connector assembly of the type described herein which permits convenient single handed-locking operation and which does not require any tools to perform the locking operation.
Briefly, in accordance with a preferred embodiment, the twist-lock connector assembly of the present invention comprises two primary components including an axially rotatable cylindrical sleeve for enclosing the insulator body portion of an electrical plug and a modified cover plate which replaces the conventional cover plate that covers the metal electrical box of a wall socket. The cylindrical sleeve has a first sleeve end that extends a distance beyond the insulator body portion of the electrical plug in the direction of the to protruding electrical conductors or prongs and a second sleeve end that is rotatably mounted to the insulator body portion of the electric plug. In use, the cylindrical sleeve is freely rotatable about the long axis of the electric plug. The first sleeve end includes a plurality of radially inwardly projecting nubs provided along an inner cylindrical surface thereof.
The modified cover plate is similar in design to a conventional cover plate except that it includes an upstanding cylindrical wall disposed about a periphery of each socket access opening. Each of the upstanding cylindrical walls is provided with a plurality of spaced apart discontinuous thread members formed along their respective exterior wall surfaces. The diameter of each upstanding cylindrical wall is dimensioned to provide a close tolerance fit within the first sleeve end of the cylindrical sleeve. Also, the thread members on the exterior wall surfaces are designed to matingly engage the nubs on the inner cylindrical surface of the first sleeve end as the sleeve is twist-rotated over the upstanding cylindrical wall.
In use, the electrical plug is inserted into the socket portion of the wall outlet and the cylindrical sleeve is rotated about a xc2xc turn. This causes the inner disposed nubs of the sleeve to lockingly engage the outer disposed threads of the upstanding cylindrical wall of the cover plate. The electrical plug is prevented from being accidentally pulled loose from the outlet by its connection with the second sleeve end of the cylindrical sleeve.
An advantage of the present invention over of the thread-in-groove twist-lock connector designs of the prior art is that the use of projecting nubs on the sleeve instead receiving grooves substantially eliminates the aforementioned problem of dirt and debris collecting in the sleeve and inhibiting positive twist-locking engagement of the locking structure.
The location of the rotatable sleeve on the electrical plug also advantageously facilitates single-handed twist-locking operation by a user.
In an alternate embodiment of the invention, the twist-lock connector assembly comprises three components: namely, a cover plate for attaching to a wall socket, a shortened cylindrical sleeve, and an adapter or face plate that attaches to or forms an integral part of the prong end of the electrical plug. The shortened cylindrical sleeve includes a first sleeve end adapted for snap fit insertion into the socket access openings of the cover plate and a second sleeve end having a plurality of spaced apart nubs disposed along an inner cylindrical surface thereof. Once snap fitted in place on the cover plate, the shortened cylindrical sleeve is permitted to axially rotate with respect to the cover plate. The face plate on the prong end of the electrical plug is provided with a plurality of external threads. In use, the electrical plug is plugged into the socket portion of the wall outlet and the shortened cylindrical sleeve is rotated so that the internally disposed nubs on the second sleeve inner cylindrical surface lockingly engage the external threads on the face plate of the electrical plug.
In still another embodiment of the invention, the twist-lock connector assembly includes a rotatable sleeve housing for enclosing the electrical plug. The rotatable sleeve includes external threads formed along a forward end portion thereof. The twist-lock connector assembly also includes a modified wall socket cover plate having socket receiving holes provided with spaced apart, inwardly projecting nubs formed integral along an inner cylindrical wall surrounding each of the socket receiving holes. In use, the conductor prongs of the electrical plug are inserted into the corresponding receiving holes of the wall socket and the sleeve is rotated thereby causing the external threads of the rotatable sleeve to lockingly engage the nubs of the cover plate.
In yet another embodiment of the invention, the twist-lock connector assembly is adapted for maintaining engagement of an electrical plug with a female socket end of an extension cord.
Another advantage afforded by the present invention is the extended operating life and reliability of the electrical contacting components of the electrical plug and socket assemblies since the twist-lock feature of the connector assembly substantially reduces tensional forces on the electrical plug and thereby prevents excess wear of the electrical contact surfaces of the female socket and male electrical plug assemblies.
Methods and apparatus which incorporate the features described above and which are effective to function as described above constitute specific objects of this invention.
Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings, which by way of illustration, show preferred embodiments of the present invention and the principles thereof and what are now considered to be the best modes contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.